Low friction cannula seals for minimally invasive robotic surgery

ABSTRACT

Embodiments of a cannula seal are disclosed. In some embodiments, a cannula seal can include a base portion that engages with a cannula; and a seal portion integrally formed with the base portion that slidebly engages with an instrument shaft such that an insertion frictional force between the seal portion and the instrument shaft for insertion of the instrument shaft is symmetrical and substantially equal with a retraction frictional force.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/599,288, filed on Feb. 15, 2012, which is herein incorporated byreference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention are related to seals, and inparticular to cannula seals for minimally invasive robotic surgery.

DISCUSSION OF RELATED ART

Surgical procedures can be performed through a surgical robot in aminimally invasive manner. The benefits of a minimally invasive surgeryare well known and include less patient trauma, less blood loss, andfaster recovery times when compared to traditional, open incisionsurgery. In addition, the use of robot surgical systems (e.g.,teleoperated robotic systems that provide telepresence), such as the daVinci® Surgical System manufacture by Intuitive Surgical, Inc. ofSunnyvale, Calif., is known. Such robotic surgical systems may allow asurgeon to operate with intuitive control and increased precision whencompared to manual minimally invasive surgeries.

In a minimally invasive surgical system, surgery is performed by asurgeon controlling the robot. The robot includes one or moreinstruments that are coupled to robot arms. The instruments access thesurgical area through small incisions through the skin of the patient. Acannula is inserted into the incision and a shaft of the instrument canbe inserted through the cannula to access the surgical area. A sealbetween the cannula and the instrument shaft allows the incision to besealed during the surgery. Existing cannula seals may have excessive,variable and direction dependent friction that can interfere with finepositioning and force sensing of the instrument tip in theinsertion-retraction direction as it contacts surgical patient anatomy.

Therefore, there is a need to develop better performing cannula sealsfor robotic minimum invasive surgeries.

SUMMARY

In accordance with aspects of the present invention, a cannula seal caninclude a base portion that engages with a cannula; and a seal portionintegrally formed with the base portion that slidebly engages with aninstrument shaft such that an insertion frictional force between theseal portion and the instrument shaft for insertion of the instrumentshaft is substantially symmetrical and substantially equal with aretraction frictional force. In some embodiments, the frictional forcesbetween the instrument shaft and the cannula seal can be substantiallyreduced.

A method of symmetrically sealing a cannula can include providing a baseportion that attaches to a cannula; and providing a sealing portionintegrally formed with the base portion that engages with an instrumentshaft such that an insertion frictional force between the seal portionand the instrument shaft for insertion of the instrument shaft issubstantially symmetrical with a retraction frictional force.

A surgical system according to some embodiments of the present inventioncan include a robotic controller; a robot arm coupled to the roboticcontroller; a surgical instrument coupled to the robot arm andcontrolled by the robotic controller, the surgical instrument includingan instrument shaft and a force sensor; a cannula coupled to the robotarm and receiving the instrument shaft of the surgical instrument; and acannula seal attached to the cannula and engaging the instrument shaftof the surgical instrument, the cannula seal including a base portionthat engages with the cannula and a seal portion integrally formed withthe base portion that slidebly engages with the instrument shaft suchthat an insertion frictional force between the seal portion and theinstrument shaft is substantially symmetrical and substantially equalwith a retraction frictional force. In some embodiments, the roboticcontroller executes code that receives force measurements from the forcesensor, corrects the force measurements for friction between the cannulaseal and the instrument shaft, and transmits corrected force feedback tomaster tool manipulators on the robot controller.

These and other embodiments are further discussed below with respect tothe following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C illustrate components of an example teleoperatedrobotic surgical system.

FIG. 2 illustrates cannulas as utilized by the system of FIGS. 1A, 1B,and 1C.

FIGS. 3A and 3B illustrate a conventional cannula seal.

FIGS. 4A and 4B illustrate a cannula seal according to some embodimentsof the present invention.

FIGS. 5A and 5B illustrate a cannula seal according to some embodimentsof the present invention.

FIGS. 6A, 6B, and 6C illustrate cannula seals according to someembodiments of the present invention.

FIGS. 7A, 7B, and 7C illustrate cannula seals according to someembodiments of the present invention.

FIGS. 8A and 8B illustrate cannula seals according to some embodimentsof the present invention.

FIGS. 9A and 9B illustrate a force sensing process according to someembodiments of the present invention.

FIG. 9C illustrates a surface contact between a seal as shown in FIG. 9Aand an instrument shaft.

DETAILED DESCRIPTION

In the following description, specific details are set forth describingsome embodiments of the present invention. It will be apparent, however,to one skilled in the art that some embodiments may be practiced withoutsome or all of these specific details. The specific embodimentsdisclosed herein are meant to be illustrative but not limiting. Oneskilled in the art may realize other elements that, although notspecifically described here, are within the scope and the spirit of thisdisclosure.

This description and the accompanying drawings that illustrate inventiveaspects and embodiments should not be taken as limiting—the claimsdefine the protected invention. Various mechanical, compositional,structural, and operational changes may be made without departing fromthe spirit and scope of this description and the claims. In someinstances, well-known structures and techniques have not been shown ordescribed in detail in order not to obscure the invention.

Additionally, the drawings are not to scale. Relative sizes ofcomponents are for illustrative purposes only and do not reflect theactual sizes that may occur in any actual embodiment of the invention.Like numbers in two or more figures represent the same or similarelements.

Further, this description's terminology is not intended to limit theinvention. For example, spatially relative terms—such as “beneath”,“below”, “lower”, “above”, “upper”, “proximal”, “distal”, and thelike—may be used to describe one element's or feature's relationship toanother element or feature as illustrated in the figures. Thesespatially relative terms are intended to encompass different positions(i.e., locations) and orientations (i.e., rotational placements) of adevice in use or operation in addition to the position and orientationshown in the figures. For example, if a device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be “above” or “over” the other elements or features.Thus, the exemplary term “below” can encompass both positions andorientations of above and below. A device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly. Likewise, descriptionsof movement along and around various axes includes various specialdevice positions and orientations. In addition, the singular forms “a”,“an”, and “the” are intended to include the plural forms as well, unlessthe context indicates otherwise. And, the terms “comprises”,“comprising”, “includes”, and the like specify the presence of statedfeatures, steps, operations, elements, and/or components but do notpreclude the presence or addition of one or more other features, steps,operations, elements, components, and/or groups. Components described ascoupled may be electrically or mechanically directly coupled, or theymay be indirectly coupled via one or more intermediate components.

Elements and their associated aspects that are described in detail withreference to one embodiment may, whenever practical, be included inother embodiments in which they are not specifically shown or described.For example, if an element is described in detail with reference to oneembodiment and is not described with reference to a second embodiment,the element may nevertheless be claimed as included in the secondembodiment.

Aspects of embodiments of the invention are described within the contextof an implementation using a da Vinci® Surgical System (specifically, aModel IS3000, marketed as the da Vinci® Si™ HD™ Surgical System),manufactured by Intuitive Surgical, Inc. of Sunnyvale, Calif.Knowledgeable persons will understand, however, that inventive aspectsdisclosed herein may be embodied and implemented in various ways,including robotic and non-robotic embodiments and implementations.Implementations on da Vinci® Surgical Systems (e.g., the Model IS3000;the Model IS2000, marketed as the da Vinci® S™ HD™ Surgical System) aremerely exemplary and are not to be considered as limiting the scope ofthe inventive aspects disclosed herein. In particular, some embodimentsof the invention assist in better force calculations along a surgicalinstrument in order to provide force feedback on the controls to asurgeon utilizing the surgical robot.

FIGS. 1A, 1B, and 1C are front elevation views of three main componentsof a teleoperated robotic surgical system for minimally invasivesurgery. These three components are interconnected so as to allow asurgeon, with the assistance of a surgical team, to perform diagnosticand corrective surgical procedures on a patient.

FIG. 1A is a front elevation view of the patient side cart component 100of, for example, the da Vinci® Surgical System. The patient side cartincludes a base 102 that rests on the floor, a support tower 104 that ismounted on the base 102, and several arms that support surgical tools.As shown in FIG. 1A, arms 106 a, 106 b, and 106 c are instrument armsthat support and move the surgical instruments used to manipulatetissue. Arm 108, for example, can be a camera arm that supports andmoves an endoscope instrument 112. Instrument arm 106 c can be anoptional third instrument arm 106 c that is supported on the back sideof support tower 104 and that can be positioned to either the left orright side of the patient side cart as necessary to conduct a surgicalprocedure. FIG. 1A further shows interchangeable surgical instruments110 a,110 b,110 c mounted on the instrument arms 106 a,106 b,106 c, andit shows endoscope 112 mounted on the camera arm 108. Knowledgeablepersons will appreciate that the arms that support the instruments andthe camera may also be supported by a base platform (fixed or moveable)mounted to a ceiling or wall, or in some instances to another piece ofequipment in the operating room (e.g., the operating table). Likewise,they will appreciate that two or more separate bases may be used (e.g.,one base supporting each arm).

As is further illustrated in FIG. 1A, instruments 110 a, 110 b, 110 c,and endoscope 112 include an instrument interface 150 a, 150 b, 150 c,and 150 d, respectively, and an instrument shaft 152 a, 152 b, 152 c,and 152 d, respectively. In some embodiments, component 100 can includesupports for cannulas that fix instruments 110 a, 110 b, 110 c, andendoscope 112 with respect to the cannulas.

Further, portions of each of the instrument arms 106 a, 106 b, and 106 care adjustable by personnel in the operating room in order to positioninstruments 110 a, 110 b, and 110 c with respect to a patient. Otherportions of arms 106 a, 106 b, and 106 c are actuated and controlled bythe surgeon at a surgeon's console 120. Surgical instruments 110 a, 110b, 110 c, and endoscope 112, can also be controlled by the surgeon atsurgeon's console 120.

FIG. 1B is a front elevation view of a surgeon's console 120 componentof the da Vinci® Surgical System. The surgeon's console is equipped withleft and right multiple DOF master tool manipulators (MTM's) 122 a,122b, which are kinematic chains that are used to control the surgicaltools. The surgeon grasps a pincher assembly 124 a,124 b on each MTM122, typically with the thumb and forefinger, and can move the pincherassembly to various positions and orientations. When a tool control modeis selected, each MTM 122 is coupled to control a correspondinginstrument arm 106 for the patient side cart 100. For example, left MTM122 a may be coupled to control instrument arm 106 b and instrument 110a, and right MTM 122 b may be coupled to control instrument arm 106 band instrument 110 b. If the third instrument arm 106 c is used during asurgical procedure and is positioned on the left side, then left MTM 122a can be switched between controlling arm 106 a and instrument 110 a tocontrolling arm 106 c and instrument 110 c. Likewise, if the thirdinstrument arm 106 c is used during a surgical procedure and ispositioned on the right side, then right MTM 122 a can be switchedbetween controlling arm 106 b and instrument 110 b to controlling arm106 c and instrument 110 c. In some instances, control assignmentsbetween MTM's 122 a,122 b and arm 106 a/instrument 110 a combination andarm 106 b/instrument 110 b combination may also be exchanged. This maybe done, for example, if the endoscope is rolled 180 degrees, so thatthe instrument moving in the endoscope's field of view appears to be onthe same side as the MTM the surgeon is moving. The pincher assembly istypically used to operate a jawed surgical end effector (e.g., scissors,grasping retractor, needle driver, and the like) at the distal end of aninstrument 110.

In accordance with certain aspects of the present invention, MTM's 122a, 122 b can provide haptic force feedback to the surgeon. This forcefeedback allows the surgeon to more accurately control the MTM's so asto operate the jawed surgical end effectors of instruments 110 a, 110 band 110 c. Accurate sensing of forces on instruments 110 a, 110 b and110 c allows for a reliable force feedback, which allows the surgeon tomore accurately control instruments 110 a, 110 b and 110 c.

Surgeon's console 120 also includes a stereoscopic image display system126. Left side and right side images captured by the stereoscopicendoscope 112 are output on corresponding left and right displays, whichthe surgeon perceives as a three-dimensional image on display system126. In an advantageous configuration, the MTM's 122 are positionedbelow display system 126 so that the images of the surgical tools shownin the display appear to be co-located with the surgeon's hands belowthe display. This feature allows the surgeon to intuitively control thevarious surgical tools in the three-dimensional display as if watchingthe hands directly. Accordingly, the MTM servo control of the associatedinstrument arm and instrument is based on the endoscopic image referenceframe.

The endoscopic image reference frame is also used if the MTM's 122 areswitched to a camera control mode. In the da Vinci® Surgical System, ifthe camera control mode is selected, the surgeon may move the distal endof the endoscope by moving one or both of the MTM's 122 together(portions of the two MTM's 122 may be servomechanically coupled so thatthe two MTM portions appear to move together as a unit). The surgeon maythen intuitively move (e.g., pan, tilt, zoom) the displayed stereoscopicimage by moving the MTM's 122 as if holding the image in the hands.

The surgeon's console 120 is typically located in the same operatingroom as the patient side cart 100, although it is positioned so that thesurgeon operating the console is outside the sterile field. One or moreassistants typically assist the surgeon by working within the sterilesurgical field (e.g., to change tools on the patient side cart, toperform manual retraction, etc.). Accordingly, the surgeon operatesremote from the sterile field, and so the console may be located in aseparate room or building from the operating room. In someimplementations, two consoles 120 (either co-located or remote from oneanother) may be networked together so that two surgeons cansimultaneously view and control tools at the surgical site.

FIG. 1C is a front elevation view of a vision cart component 140 of theda Vinci® Surgical System. The vision cart 140 houses the surgicalsystem's central electronic data processing unit 142 and visionequipment 144. The central electronic data processing unit includes muchof the data processing used to operate the surgical system. In variousother implementations, however, the electronic data processing may bedistributed in the surgeon console and patient side cart. The visionequipment includes camera control units for the left and right imagecapture functions of the stereoscopic endoscope 112. The visionequipment also includes illumination equipment (e.g., Xenon lamp) thatprovides illumination for imaging the surgical site. As shown in FIG.1C, the vision cart includes an optional 24-inch touch screen monitor146, which may be mounted elsewhere, such as on the patient side cart100. The vision cart 140 further includes space 148 for optionalauxiliary surgical equipment, such as electrosurgical units andinsufflators. The patient side cart and the surgeon's console arecoupled via optical fiber communications links to the vision cart sothat the three components together act as a single teleoperatedminimally invasive surgical system that provides an intuitivetelepresence for the surgeon. And, as mentioned above, a secondsurgeon's console may be included so that a second surgeon can, e.g.,proctor the first surgeon's work.

During a typical surgical procedure with the robotic surgical systemdescribed with reference to FIGS. 1A-1C, at least two incisions are madeinto the patient's body (usually with the use of a trocar to place theassociated cannula). One incision is for the endoscope camerainstrument, and the other incisions are for the surgical instruments. Insome surgical procedures, several instrument and/or camera ports areutilized to provide access and imaging for a surgical site. Although theincisions are relatively small in comparison to larger incisions usedfor traditional open surgery, a minimum number of incisions is desiredto further reduce patient trauma and for improved cosmesis.

FIG. 2 illustrates utilization of the surgical instrument illustrated inFIGS. 1A, 1B, and 1C. As shown in FIG. 2, shafts 152 a, 152 b, and 152 dpass through cannulas 202 a, 202 b, and 202 c, respectively. Cannulas202 a, 202 b, and 202 c extend through instrument incisions 204 a, 204b, and 204 c, respectively. As is shown in FIG. 2, shafts 152 a, 152 b,and 152 d extend through cannulas 202 a, 202 b, and 202 c, respectively.End effectors 206 a, 206 b, and 206 c are attached to shafts 152 a, 152b, and 152 d, respectively. As discussed above, end effectors 206 a, and206 b can be jawed surgical end effectors (e.g., scissors, graspingretractor, needle driver, and the like). Further, end effector 206 c isillustrated as an endoscope tip. As shown in FIG. 2, cannulas 202 a, 202b, and 202 c and shafts 152 a, 152 b, and 152 d are positioned so thatend effectors 206 a, 206 b, and 206 c operate in a surgical area 210.

As shown in FIG. 2 cannulas 202 a, 202 b, and 202 c include mountingfittings 208 a, 208 b, and 208 c, respectively, that can be engaged byarms 106 a, 106 b, and endoscope arm 108, respectively, to allow forvery little movement of the instrument end effectors 206 a, 206 b, and206 c, respectively, as possible. Cannulas 202 a, 202 b, and 202 cfurther include cannula seal mounts 212 a, 212 b, and 212 c,respectively.

Cannula seals mounted to cannula seal mounts 212 a, 212 b, and 212 cprevent leakage around shafts 152 a, 152 b, and 152 d, respectively.During surgery, particularly if the surgery is abdominal surgery,pressurized CO₂ can be utilized to expand the abdomen, allowing forbetter access to surgical area 210. Further, cannula seals attached tocannula seal mounts 212 a, 212 b, and 212 c prevent leakage of fluids orother materials from the patient.

During the operation, the surgeon sitting at surgeon's console 120 canmanipulate end effectors 206 a, 206 b, and 206 c as well as move shafts152 a, 152 b, and 152 d along force lines Fa, Fb, and Fc, respectively.These force lines represent forces along the insertion/retractiondirection (i.e., the direction along shaft 152). Collectively, whetherinsertion or retraction, this direction may be referred to as theinsertion direction.

As shown in FIG. 9A, utilizing various force measuring devices 904, theforces on end effectors 206 a, 206 b, and 206 c can be utilized toprovide force feedback to the surgeon at console 120, usually throughresistance to the surgeon's input at MTMs 122, to allow the surgeon tocontrol the force applied to end effectors 206 a, 206 b, and 206 c. FIG.9A also illustrates a cannula seal 902 according to some embodiments ofthe present invention sealing shaft 152 and engaging cannula mount 212.

Effective surgical instrument force feedback utilizes a full 3dimensional sensing of the forces at end effectors 206 (collectivelyreferring to end effectors 206 a, 206 b, and 206 c). While satisfactoryinstrument shaft mounted force transducers provide good feedback for thetransverse surgical forces applied to patient tissue through wrists andjaws of end effectors 206, wrist actuation cable forces utilized tooperate end effectors 206 may prevent accurate sensing of surgicalforces in the insertion direction (i.e., the direction along shafts 152(collectively referring to shafts 152 a, 152 b, 152 c, and 152 d). As aresult, insertion direction forces are typically sensed at the back ofsurgical instruments 110 (collectively referring to surgical instruments110 a, 110 b, 110 c, and endoscope 112) at instrument interface 150(collectively referring to instrument interfaces 150 a, 150 b, 150 c,and 150 d) or on arm 106 (collectively referring to arms 106 a, 106 b,and 106 c or endoscope 112). In those cases, the frictional forces ofshaft 152 sliding through cannula seals 902 mounted to cannula sealmount 212 (collectively referring to cannula seals mounts 212 a, 212 b,and 212 c) becomes important, especially if that frictional force varieswith direction (insertion or retraction), or velocity of shaft 152through seal 212. In the discussion below, unequal insertion directionforces will be referred to as asymmetric while equal insertion andretraction forces will be referred to as symmetric. Cannula sealfeatures in sliding contact with an inserted instrument shaft will alsobe referred to as symmetric when similar features face in oppositedirections along the insertion direction or when such features do notpoint either way. Some embodiments of the present invention includecannula seal 902 that substantially reduces or eliminates thedirectional or velocity dependence in the shaft seal frictional forcemeasured by the force sensing devices, and therefore allow for moreaccurate feedback of forces to the operating surgeon. In someembodiments, cannula seal 902 may include a pressurized seal where thefrictional forces along the insertion direction are substantially zero.

Cannula seals have taken a number of forms including simpleunidirectional compliant lip seals, tri-cuspid or multi-cuspid radialleaf seals, and spirally stacked overlapping and/or folded seal leavesakin to a traditional camera lens iris. Each of these types of sealshave asymmetric construction which causes unequal seal frictional forcedepending on the direction of motion.

FIGS. 3A and 3B illustrate a conventional cannula seal 302. As shown inFIG. 3A, cannula seal 302 includes a base portion 306 and a retainingportion 308. Base portion 306 is attachable to cannula 202 at cannulaseal mount 212 and is held in place by retaining portion 308, which isintegrally formed with base portion 306. Retaining portion 308 alsoprovides for sealing against cannula seal mount 212.

Further, cannula seal 302 includes a seal lip 304 that seals aroundshaft 152. FIG. 3B illustrates lip 304 sealing around shaft 152. As isillustrated in FIGS. 3A and 3B, lip 304 is asymmetric and is oriented inthe insertion direction. Thus, shaft 152 will experience a differentfrictional force based on direction of motion. As is illustrated in FIG.3B, lip 304 is oriented in a direction that facilitates motion of shaft152 the insertion direction. However, in the retraction direction,friction with shaft 152 compresses lip 304 about shaft 152 causing amuch higher frictional force. In some cases, the ratio in force betweeninsertion and retraction of shaft 152 can be a factor of about 1.5.

In some cases, especially with abdominal surgery, the direction of 11 p304 assists in sealing against insufflation pressure. In abdominalsurgery, pressurized CO₂ is provided into the abdomen by an insufflationsystem in order to expand the abdomen. CO₂ utilized in the insufflationsystem is typically supplied by a pressurized CO₂ tank and a regulator.The CO₂ pressure in the abdomen will load lip 304 by providing a forcethat pushes lip 304 more firmly against shaft 152.

Some other cannula seals have two transversely opposing lips like ashortened version of an oboe reed. Yet other seals have a simplecompliant circular hole in a diaphragm. In this case, the deflectiondirection of the seal inverts, the result being that the seal lip facesin the direction opposite where it started, when motion of the shaftthrough the seal reverses direction, causing further uneven insertionfriction force effects. Still other designs rely on an open complianthole with a rigid plastic door that is pushed aside when the instrumentshaft pass through the seal. In this case, the hinge direction of thedoor exerts asymmetric direction dependent friction forces on theinstrument. In every case of existing seals, the forces are excessive,direction dependent, and vary too much with operating conditions topermit motion direction based subtraction of the expected frictionforces from sensed forces to null out the frictional effects. Theexpected friction force contribution may be based on experimentalmeasurements. Therefore, utilizing these seals, the frictional forceprovides for unreliable force feedback to the surgeon.

Other than the application of lubricant, this problem has not beenaddressed. Some manufacturers of laparoscopic cannula seals provide aseparately packaged pouch of lubricant such as silicone or purified(white mineral oil based) petroleum grease for optional use or pre-coatthe seal with such a grease. Silicone or other rubber materials utilizedas a seal have a relatively high dry coefficient of friction. Greaselubricants help but do not sufficiently reduce seal friction and maywipe off during a procedure so that the friction varies with time.Grease lubricants also do not equalize the direction dependent forcesdue to asymmetric seal lip design. Therefore, addition of lubricatingmaterials alone does not significantly help with the asymmetricfrictional forces applied when the instrument shaft is moved through aseal.

In some embodiments, the noise limited force sensitivity of a transverseinstrument force transducer allows measurement of forces significantlylower than the frictional forces on existing cannula seals. Therefore,the combined effect of all parasitic insertion forces on instrument 110between a shaft face 152 and cannula seal 902 may be greater than thetransverse force transducer sensitivity. It may be possible to improvethe transverse force sensitivity further in the future, resulting in aneed for a similar improvement in the force sensitivity in the axialdirection. Greased seals in combination with present seal designs cannotaccomplish the sensitivity needed to provide for reliable force feedbackto the surgeon.

Experimental coating of existing molded silicone rubber seals with a drylubricant parylene managed to reduce the friction between the shaft andthe seal by a factor of approximately 4 as opposed to the uncoated seal.The force can be measured with a handheld force gauge. However, theasymmetric nature of the friction caused by conventional seal lipscauses a difference in the friction depending on the direction of motionof the shaft through the seal. This asymmetric nature detrimentallyaffects the ability of the force applied at the effector to bedetermined by the surgeon.

In particular, in order to provide for a highly reliable indication ofthe force along shaft 152, both in insertion and retraction, it isdesirable that the frictional force between cannula seal 902 attached tocannula seal mount 212 be as symmetric as possible with respect todirection of motion and as uniform as possible during motion. In thatcase, an estimate of the frictional force can be subtracted from theinsertion direction forces measured by a sensor. It is also desirablethat the frictional force be as low as possible in order to minimize anyremaining error in the improved estimate of the insertion directionsurgical force on patient tissue obtained by subtracting the estimatedfriction force from the sensor measured force.

FIGS. 4A and 4B illustrate a cannula seal 402 that can be utilized ascannula seal 902 according to some embodiments of the present invention.As shown in FIG. 4A, cannula seal 402 includes base portion 406 and asealing portion foamed of lips 404 a and 404 b. Base portion 406 mayinclude a feature 408 that engages seal retainer 212 of cannula 202. Inthe embodiment of seal 402 illustrated in FIGS. 4A and 4B, sealingportion lips 404 a and 404 b are integrally formed, symmetric oppositelyoriented lips that seal around shaft 152. As shown in FIG. 4B, lips 404a and 404 b are oriented such that lip 404 a provides relatively lowfriction (lower than lip 404 b) in the insertion direction and lip 404 bprovides relatively low friction (lower than lip 404 a) in theretraction direction. In that fashion, insertion of shaft 152 andretraction of shaft 152 both experience substantially the samefrictional force from seal 402. In that fashion, theinsertion/retraction force for shaft 152 can be better calculated.

Lips 404 a and 404 b can be placed in a range of positions with respectto one another and may be substantially identically constructed. Theymay be separated from each other by a range of distances and may beoriented so that the seal lips point toward each other as shown in FIGS.6A and 6B rather than away from each other as shown in FIGS. 4A and 4B.The frictional force resulting from seal 402 with lips 404 a and 404 bmay be substantially symmetrical, however insufflation pressure insidethe body will load lip 404 a greater than lip 404 b. As a result, withthe embodiment illustrated in FIG. 4B, there may be a difference in thefrictional force experienced depending on insertion or retraction ofshaft 152.

Lips 404 a and 404 b can be characterized by the parameters b and a. Inthis case, b is the axial distance from where seal lip 404 a or 404 bconnects to base 406 of seal 402 to where seal lip 404 a or 404 bcontacts a wall of shaft 152. Then a is the radial distance from whereseal lip 404 a or 404 b connects to base 406 of seal 402 to the wall ofshaft 152 when seal 402 is engaged by shaft 152. A longer b will providemore radial compliance and maintain sealing contact with the wall ofshaft 152 with less force variation over a greater range of eccentricmisalignment of the seal 402 and the shaft 152. Longer b may alsoprovide a higher loading effect from insufflation, for example. Longer bmay also provide a better seal. A smaller dimension a results in areduced moment arm for insertion friction forces between the seal lips404 a and 404 b and shaft 152. This means that there is less increase inthe lip contact force with shaft 152 and less self-amplification of thefriction force in the direction of motion opposite the orientation of aseal lip.

It is possible to alter the seal lip dimension b of one of seal lips 404a and 404 b to compensate for the unequal effect of insufflationpressure on the friction force of identical oppositely facing seal lips.For example, if dimension b is made slightly less for seal lip 404 athan for seal lip 404 b then the insufflation pressure induced increasein seal friction on seal lip 404 a can be reduced so that the summedseal lip friction forces are equal in both directions of motion. Thiswill further improve the ability to reduce seal friction induced errorsin the estimated insertion axis tissue forces to be fed back to thesurgeon through MTM's 122.

Friction in seal 402 can be reduced by lubrication as discussed above.Furthermore, friction in seal 402 can be reduced by texturing lips 404 aand 404 b, for example by providing a pebbled or rounded surface textureto lips 404 and 406. Textured surfaces may provide less friction whilealso providing a good seal between lips 404 a and 404 b and the wall ofshaft 152. Lubrication such as parylene can be applied to seal 402 inorder to reduce friction. Reduction in the friction along the insertiondirection can help to provide more accurate force calculations byreducing the size of the friction correction to the sensor measuredforce and, if there is any asymmetry remaining in the frictional force,reducing the error in that correction.

The embodiments of seal 402 shown in FIGS. 4A and 4B are examples of aseal according to the present invention. Embodiments of the presentinvention provide symmetric sealing in that the insertion and retractionfrictional forces are substantially the same. Although insufflation maycause some asymmetry in the frictional force to remain, that asymmetrywill be within the range that still results in reliable force feedbackto the surgeon or, in some embodiments, seal 402 may be modified suchthat the frictional forces on insertion and retraction are closer tobeing the same. In that fashion, the frictional forces can bepredictable and subtracted from sensor measured forces in a calculationof the forces applied to shaft 152 so that a surgeon sitting at console120 can have a reliable feedback of forces applied to shaft 152.

FIGS. 5A and 5B illustrate another embodiment of seal 902, a seal 502.As illustrated in FIG. 5A, seal 502 includes a hose connection 514 and achannel 512 that provides pressurized fluid to an annular cavity 510that is formed between lips 504 a and 504 b and surrounding shaft 152.The pressurized fluid applied to cavity 510 can include CO₂, salinesolution, air, or other fluids. During surgery, the abdomen of thepatient may be inflated with pressurized CO₂ in order to provide moreroom in the surgical area for the surgical instruments. If CO₂ isprovided at into cavity 510 at a pressure greater than that of thepressure in the surgical area, then lips 504 a and 504 b can be liftedfrom the wall of shaft 152 to form gaps 516 a and 516 b, respectively.In gaps 516 a and 516 b, a pressure seal can be formed. One advantage offorming such a pressure seal is that the frictional forces between seal502 and shaft 152 are substantially eliminated. Further, such a pressureseal effectively prevents fluids from leaking around shaft 152 duringthe surgery due to the overpressure in annular cavity 510 with respectto the insufflation pressure in the patient's body. Pressurized CO₂supplied to hose connection 514 can, for example, be provided through aseparate regulator from a pressurized tank that is also utilized toprovide pressurized CO₂ to the surgical area. In that case, the CO₂pressure is set higher than the pressure of CO₂ to the surgical area inorder to provide the pressure seal.

The pressure seal formed at gaps 516 a and 516 b allows the frictionalforce to be nearly zero. In some embodiments, cavity 510 isunpressurized, so that lips 504 a and 504 b can contact the wall ofshaft 152 and provide a contact seal. Unpressurized, the frictionalforce supplied by the embodiment of seal 502 shown in FIG. 5B issubstantially symmetric and can be lessened with the use of a lubricant.In some embodiments, lips 504 a and 504 b may have an inner diametergreater than the diameter of shaft 152 to that lips 504 a and 504 b donot fully contact shaft 152 even when cavity 510 is unpressurizedalthough pressure greater than the insufflation pressure may still beapplied to cavity 510 to prevent leakage of fluid from the insufflatedsurgical area. In this case, the fluid pressure may cause the innersurfaces of the lips to act as a fluid bearing with nearly zero frictionagainst shaft 152.

FIGS. 6A and 6B illustrate another embodiment of seal 902, a seal 602that includes an opposite approach. Seal 602 includes a base portion 606and a seal portion 604. As shown in FIG. 6A, seal portion 604 includessymmetric seal lips 604 a and 604 b. Symmetric seal lips 604 a and 604 bcontact the outer wall 152 in a symmetrical fashion and providesubstantially symmetrical frictional forces along shaft 152 with respectto direction of motion. A cavity 610 may provide flexibility of sealmembers 604, resulting in a more compliant seal between seal members 604and shaft 152. As discussed above, in some embodiments the frictionalforce may be lessened with the use of a lubricant.

FIG. 6C illustrates another embodiment of seal 602. As shown in FIG. 6C,seal 602 may include a channel 612 and a hose connection 614 so thatpressurized fluid may be utilized to pressurize cavity 610. Seal 602 mayhave an initial diameter clearance with respect to shaft 152 to insureminimum initial friction. As shown in FIG. 6C, pressurizing cavity 610may help lips 604 a and 604 b to controllably engage the wall of shaft152 sufficiently to insure a seal while still reducing friction comparedto a seal designed for initial diameter interference with shaft 152. Theelevated pressure in space 610 above the pressure in the patient's bodycavity further aids the sealing effect because gas cannot flow from thelower pressure in the patient's body toward the higher pressure in sealcavity 610 adjacent the shaft 152.

Again in the embodiment illustrated in FIGS. 6A, 6B, and 6C in someembodiments an asymmetric frictional force caused by insufflation gaslifting lip 604 a from shaft 152 may be compensated for by adjusting thedimensions of lips 604 a and 604 b accordingly. Further, frictionalforces may be reduced with lubrication or by providing a texturedsurface on lips 604 a and 604 b where shaft 152 is contacted.

FIGS. 7A and 7B illustrate another embodiment of seal 902, a seal 702that includes another approach. Seal 702 includes a base portion 706 anda seal portion 704. As shown in FIG. 7A, seal portion 704 provides asymmetric radially compliant seal surface. The symmetrical seal surface704 contacts the outer wall 152 and provides substantially equalfrictional forces along shaft 152 independent of motion direction. Acavity 710 provides radial flexibility of seal member 704, resulting ina more compliant seal between seal member 704 and shaft 152. Asdiscussed above, in some embodiments the frictional force may belessened with the use of a lubricant such as a grease or a pebbletextured seal surface.

FIG. 7C illustrate an embodiment of seal 702 where cavity 710 can bepressurized. As shown in FIG. 7C, a channel 712 and hose connection 714can be utilized to pressurize cavity 710. Seal 702 may be designed withinitial diameter clearance with respect to shaft 152 to insure minimuminitial friction. Pressurizing cavity 710 can help seal surface 704controllably engage the wall of shaft 152 to provide sufficient contactforce for adequate seal without excessive contact force that may provideunacceptable frictional forces on shaft 152.

In each of the embodiments of seal 902 (seals 402, 502, 602, and 702),seal surfaces 404, 504, 604 and 704, respectively, and shaft 152 can becoated with a lubricant such as Parylene. Parylene substantially lowersany remaining friction and exhibits almost no stiction (e.g., nodifference between static friction and dynamic friction). Otherlubricants, for example medical grade petroleum based lubricants orsilicone based lubricants, can be utilized. Further, as discussed above,texturing of seal member 404, 504, 604 and 704 or shaft 152 may alsolower the frictional force.

FIGS. 8A and 8B illustrate another embodiment of seal 902, a seal 802,that includes another approach. Seal 802 includes a base portion 806 anda seal portion 804. As shown in FIG. 8A, seal portion 804 provides asymmetric radially compliant seal surface. The symmetriccircumferentially grooved cylindrical seal surface of 804 contacts theouter wall of shaft 152 and provides substantially equal frictionalforces along shaft 152 independent of motion direction. Seal portion 804may be made of a low friction polymer material such as PTFE insertmolded or otherwise retained inside an elastomer seal body 802. Grooves810 improve the sealing characteristics of the smooth lip-less sealdesign. A gap 812 permits a close fit without binding or excessivefriction between the seal portion 804 and instrument shaft surface 152in the case of tolerance variations in the respective diameters. Gap 812can be any opening, for example a longitudinal or helical opening,intersecting grooves 810. The compliant elastomer material of seal 802helps portion 804 conform to shaft 152 for the best seal. In someembodiments, grooves 810 may be pressured as discussed above.

FIGS. 9A and 9B illustrate measurement of the insertion force in orderto provide feedback to a surgeon utilizing MTMs 122 at console 120. Asshown in FIG. 9A, cannula seal 902, which may be one of seals402,502,602,702, or 802) according to some embodiments of the presentinvention is attached to cannula 202. As such, cannula seal 902 exhibitssubstantially symmetric frictional forces with regard to both theinsertion and retraction directions. Shaft 152 extends through cannula202 so that cannula seal 902 engages shaft 152 as discussed above andend effector 206 is exposed. A force sensor 904 is coupled withinstrument interface 150 or mounted on instrument arm 106. Force sensor904 communicates force readings to data processing unit 142, whichcomputes the force feedback to apply to MTM 122 of surgeon's console120. Force sensor 904 can be any device capable of detecting the axialforce applied to shaft 152, for example a conventional strain gage forcetransducer, a piezoelectric element, an optical fiber strain gauge, orother device.

FIG. 9C illustrates a surface contact between seal 902 and a shaft 152according to some embodiments of the invention. As discussed above, seal902, which can be one of seals 402, 502, 602, 702, and 802, can beformed of silicone rubber. Other materials that can be utilized to formseal 902 can include medical grades of urethane, Pebax, EPDM, Viton, orother TPE and rubber compounds as well as low friction polymers such asPTFE. Seal 902 according to some embodiments of the present invention,can be disposable and can be attached to cannula 202 for the duration ofa single surgery. As has been discussed above, seal 902 can be coatedwith a lubricant such as parylene to reduce frictional forces along theinsertion/retraction direction. As is illustrated in FIG. 9C, someembodiments of seal 902 may include a textured surface 906 that engagesthe inside wall of shaft 152. Textured surface 906 can help to reducethe frictional forces between seal 902 and shaft 152.

FIG. 9B illustrates an algorithm for processing the force data fromforce sensor 902. As shown in FIG. 9B, a force measurement is taken byforce sensor 904 in step 910. In step 912, the force measurement iscorrected for cannula seal friction. In step 912, the cannula sealfriction utilizing a cannula seal 902, which can be one of seals402,502,602,702,802, according to some embodiments of the presentinvention can be predictable. In some embodiments, the cannula sealfriction can be symmetric with respect to insertion and retractiondirection. In some embodiments, the cannula seal frication can besubstantially zero. In step 914, the corrected force is utilized toprovide haptic feedback to the surgeon at console 122, for example byapplying a resistance force to the motion of a MTM 122.

The above detailed description is provided to illustrate specificembodiments of the present invention and is not intended to be limiting.Numerous variations and modifications within the scope of the presentinvention are possible. The present invention is set forth in thefollowing claims.

What is claimed is:
 1. A cannula seal, comprising: a base portion thatengages with a cannula; and a seal portion integrally formed with thebase portion that slidebly engages with an instrument shaft such that aninsertion frictional force between the seal portion and the instrumentshaft for insertion of the instrument shaft is substantially symmetricaland substantially equal with a retraction frictional force.
 2. The sealof claim 1, wherein the seal portion includes a first lip and a secondlip, the first lip and the second lip being placed to engage theinstrument shaft in symmetrically opposing directions.
 3. The seal ofclaim 2, wherein the first lip is oriented in an insertion direction andthe second lip is oriented in a retraction direction that is oppositethe insertion direction, such that the first lip provides a lowerfriction against the shaft than the second lip as the shaft is moved inthe insertion direction, and the second lip provides a lower frictionagainst the shaft than the first lip when the shaft is moved in theretraction direction.
 4. The seal of claim 2, wherein the second lip isoriented in an insertion direction and the first lip is oriented in aretraction direction that is opposite the insertion direction such thatthe second lip provides a lower friction against the shaft than thefirst lip as the shaft is moved in the insertion direction, and thefirst lip provides a lower friction against the shaft than the secondlip when the shaft is moved in the retraction direction.
 5. The seal ofclaim 2, wherein the first lip and the second lip are shaped differentlyto correct for an asymmetrical aspect of the force between the sealportion and the instrument shaft for insertion and retraction.
 6. Theseal of claim 2, wherein a cavity is formed between the first lip andthe second lip and further including a hose connection integrally formedwith the base portion; and a channel formed between the hose connectionand the cavity, wherein a pressurized fluid is delivered to the cavitycontrolling friction between the seal lips and an instrument shaft. 7.The seal of claim 6, wherein the pressurized fluid is chosen from a setof fluids consisting of CO₂, air, and saline solution.
 8. The seal ofclaim 6, wherein the first lip and the second lip do not contact theshaft and sealing is formed by an overpressure in the cavity.
 9. Theseal of claim 8, wherein the first lip and the second lip do not engagethe shaft when the cavity is unpressurized.
 10. The seal of claim 1,wherein the seal portion includes a symmetric radially compliant sealsurface.
 11. The seal of claim 10, wherein the seal surface contacts anouter wall of the shaft.
 12. The seal of claim 10, wherein thesymmetrical member includes a cavity.
 13. The seal of claim 12, furtherincluding a hose connection integrally formed with the first portion;and a channel formed between the hose connection and the cavity, whereinpressurized fluid is delivered to the cavity.
 14. The seal of claim 10,wherein the symmetric radially compliant seal surface includes asymmetric circumferentially grooved cylindrical seal surface thatcontacts the outer wall of the shaft.
 15. The seal of claim 14, furtherincluding a gap intersecting the grooves for the grooved cylindricalseal surface.
 16. The seal of claim 1, wherein the seal portion includesa lubricant coating.
 17. The seal of claim 16, wherein the lubricant isparylene.
 18. The seal of claim 1, wherein the seal portion includes atextured surface that engages the instrument shaft.
 19. A method ofsymmetrically sealing a cannula, comprising: providing a base portionthat attaches to a cannula; and providing a sealing portion integrallyformed with the base portion that engages with an instrument shaft suchthat an insertion frictional force between the seal portion and theinstrument shaft for insertion of the instrument shaft is substantiallysymmetrical with a retraction frictional force.
 20. The method of claim19, wherein providing the sealing portion includes providing a first lipand a second lip, the first lip and the second lip being placed toengage the instrument shaft in symmetrically opposing directions. 21.The method of claim 20, further including providing a hose connectionand a channel formed in the base portion to direct pressure to a cavityformed between the first lip and the second lip.
 22. The method of claim21, wherein the first lip and the second lip do not contact the shaftand seal friction is controlled by the pressure between the seal lips.23. The method of claim 22, wherein sealing is formed by an overpressurein the cavity.
 24. The method of claim 19, wherein providing the sealingportion includes providing a symmetric radially compliant seal surface.25. The method of claim 24, wherein the symmetrical member includes acavity.
 26. The method of claim 25, further including providing a hoseconnection integrally formed with the first portion and a channel formedbetween the hose connection and the cavity.
 27. The method of claim 24,wherein the symmetric radially compliant seal surface includes asymmetric circumferentially grooved cylindrical seal surface thatcontacts the outer wall of the shaft.
 28. The method of claim 27,wherein the seal surface includes a gap intersecting grooves of thesymmetric circumferentially grooved cylindrical seal surface.
 29. Themethod of claim 19, further including coating the sealing portion with alubricant.
 30. The method of claim 29, wherein the lubricant isparylene.
 31. The method of claim 20, further including shaping thefirst lip and the second lip to correct for asymmetries in the insertionand retraction forces.
 32. A surgical system, comprising: a roboticcontroller; a robot arm coupled to the robotic controller; a surgicalinstrument coupled to the robot arm and controlled by the roboticcontroller, the surgical instrument including an instrument shaft and aforce sensor; a cannula coupled to the robot arm and receiving theinstrument shaft of the surgical instrument; and a cannula seal attachedto the cannula and engaging the instrument shaft of the surgicalinstrument, the cannula seal including a base portion that engages withthe cannula and a seal portion integrally formed with the base portionthat slidebly engages with the instrument shaft such that an insertionfrictional force between the seal portion and the instrument shaft issubstantially symmetrical and substantially equal with a retractionfrictional force, wherein the robotic controller executes code thatreceives force measurements from the force sensor, corrects the forcemeasurements for friction between the cannula seal and the instrumentshaft, and transmits corrected force feedback to master toolmanipulators on the robot controller.